Not a surprise - I know at the recent Rangers my BiL and nephew were surrounded by the Union Bears, many of whom were openly boasting of having "doubled up" to gain entry. This is apparently a common occurence at Rangers (and I would have to assume Celtic too) away games. How ticketless fans get that close to the stadium, let alone turnstiles astonishes me.
Certainly at the last Rangers game there was no stairway access visible in the 3 sections on the top tier, next to the East Stand.